As a conventional position determination system, a GPS (Global Positioning System) is known. A satellite for emitting a signal for use in the GPS (the satellite and the signal will hereinafter be referred to respectively as “GPS satellite” and “GPS signal”) is flying at an attitude of about twenty thousand km from the ground. Any user is allowed to receive the signal emitted from the GPS satellite so as to measure a distance between the GPS satellite and the user through demodulation of the received signal. Thus, as long as there is no obstacle between the ground and the GPS satellite, position determination can be performed using the signal emitted from the GPS satellite. However, in cases where the GPS is used, for example, in an urban area, a forest of buildings often becomes obstacle to cause a situation where a position information providing apparatus of a user cannot receive the signal emitted from the GPS satellite. Further, depending on conditions, a signal diffraction or reflection often occurs due to the buildings to cause an error in distance measurement using the signal, which leads to deterioration in accuracy of position determination.
Although there is a technique of receiving in an indoor area a weak GPS signal which has penetrated through a wall or roof, a receiving state is still unstable, which causes deterioration in accuracy of position determination.
While the above description has been made about position determination by taking the GPS as an example, the aforementioned phenomena are observed in a satellite-based positioning system in general. As used herein, the term “satellite-based positioning system” means any type of satellite-based positioning system including GLONASS (GLObal NAvigation Satellite System) in Russian Federation, and Galileo in Europe, as well as the GPS.
A technique related to a position information providing system is disclosed, for example, in JP 2006-67086A (Patent Publication 1).    Patent Publication 1: JP 2006-67086A